Angiotensin II (Ang II) has recently become recognized as a powerful pro-inflammatory mediator. Although originally appreciated for its critical role in regulating blood pressure, this peptide hormone is now known to stimulate inflammatory pathways in numerous tissues, including the heart and arteries. Chronic exposure to Ang II may then lead to a variety of pathologic conditions related to a heightened inflammatory state. Perhaps the best example is in muscular arteries, where Ang II contributes to the development of atherosclerosis by stimulating the recruitment of macrophages and other inflammatory cells, stimulating smooth muscle proliferation and activation, and promoting endothelial dysfunction. The principal receptor for Ang II (AT1R) is a member of the G protein-coupled receptor superfamily. Numerous signaling pathways are initiated following ligand activation of this receptor, but stimulation of the NF-:B transcription factor appears to underlie most of the pro-inflammatory effects of Ang II. Importantly, while activation of protein kinase C (PKC) is a prerequisite for this effect, very little is known about the intermediate steps that bridge Ang II-dependent PKC activation with the eventual stimulation of NF-:B. However, our preliminary data now reveal a molecular link to explain this phenomenon. Our data indicate that a scaffolding protein (CARMA3) serves to integrate an upstream signal from PKC with the downstream effector proteins, Bcl10 and MALT1, which together stimulate a canonical pathway for NF-:B activation. We propose to explore the physiologic and biochemical implications of this signaling pathway through 4 aims: (1) Identify the molecular mechanism by which the AT1 receptor communicates with CARMA3. (2) Identify the molecular mechanism by which the IKK complex is activated following Ang II stimulation. (3) Test the role of CARMA3, Bcl10, and MALT1 in mediating Ang II-dependent inflammatory responses in endothelial and vascular smooth muscle cells. (4) Test the role of CARMA3 in mediating Ang II-dependent cardiovascular pathology, through analysis of CARMA3 knockout mice. Project Relevance: Ang II-dependent hypertension is a major contributing factor to cardiovascular disease. Understanding the pro-inflammatory, intracellular signaling events activated by Ang II is critical for our ability to eventually control the adverse effects of Ang II. Detailed knowledge of these signaling events will allow for the rational design of pharmacologic agents to target these events.